Spring Cloud Zuul

拦截器在请求中如何起作用

// DispatcherServlet.doDispatch
    protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        HttpServletRequest processedRequest = request;
        HandlerExecutionChain mappedHandler = null;
        boolean multipartRequestParsed = false;

        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

        try {
            ModelAndView mv = null;
            Exception dispatchException = null;

            try {
                processedRequest = checkMultipart(request);
                multipartRequestParsed = (processedRequest != request);

                // 获取HandlerExecutionChain
                mappedHandler = getHandler(processedRequest);
                if (mappedHandler == null) {
                    noHandlerFound(processedRequest, response);
                    return;
                }

                // Determine handler adapter for the current request.
                HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

                // Process last-modified header, if supported by the handler.
                String method = request.getMethod();
                boolean isGet = "GET".equals(method);
                if (isGet || "HEAD".equals(method)) {
                    long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
                    if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
                        return;
                    }
                }

                // 调用interceptors中拦截器的 preHandle
                if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                    return;
                }

                // Actually invoke the handler.
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

                if (asyncManager.isConcurrentHandlingStarted()) {
                    return;
                }

                applyDefaultViewName(processedRequest, mv);
                // 调用interceptors中拦截器的 postHandle
                mappedHandler.applyPostHandle(processedRequest, response, mv);
            }
        ···省略···
    }

HandlerExecutionChain如何构建

// 首先，AbstractHandlerMapping内部的initInterceptors方法中，会遍历interceptors集合，然后判断各个项是否是MappedInterceptor、HandlerInterceptor、WebRequestInterceptor。
    @Override
    protected void initApplicationContext() throws BeansException {
        extendInterceptors(this.interceptors);
        detectMappedInterceptors(this.adaptedInterceptors);
        initInterceptors();
    }

    protected void initInterceptors() {
        if (!this.interceptors.isEmpty()) {
            for (int i = 0; i < this.interceptors.size(); i++) {
                Object interceptor = this.interceptors.get(i);
                if (interceptor == null) {
                    throw new IllegalArgumentException("Entry number " + i + " in interceptors array is null");
                }
                this.adaptedInterceptors.add(adaptInterceptor(interceptor));
            }
        }
    }

// HandlerExecutionChain的拦截器是从AbstractHandlerMapping中的adaptedInterceptors和mappedInterceptors属性中获取的
// AbstractHandlerMapping.getHandlerExecutionChain
    protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
        HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
                (HandlerExecutionChain) handler : new HandlerExecutionChain(handler));

        String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
        for (HandlerInterceptor interceptor : this.adaptedInterceptors) {
            if (interceptor instanceof MappedInterceptor) {
                MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;
                if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
                    chain.addInterceptor(mappedInterceptor.getInterceptor());
                }
            }
            else {
                chain.addInterceptor(interceptor);
            }
        }
        return chain;
    }

从HanlderInterceptor到加载WebMvcConfigurer全流程

// DelegatingWebMvcConfiguration.setConfigurers 这个类是WebMvcConfigurationSupport的子类
    // setConfigurers通过注入setConfigurers来将用户自定的configurers，放入自身属性WebMvcConfigurerComposite configurers中
    private final WebMvcConfigurerComposite configurers = new WebMvcConfigurerComposite();
    @Autowired(required = false)
    public void setConfigurers(List<WebMvcConfigurer> configurers) {
        if (!CollectionUtils.isEmpty(configurers)) {
            this.configurers.addWebMvcConfigurers(configurers);
        }
    }

// WebMvcConfigurerComposite 这里其实就是组合各个WebMvcConfigurer，从而让用户可以实现配置多个WebMvcConfigurer
    private final List<WebMvcConfigurer> delegates = new ArrayList<>();

    public void addWebMvcConfigurers(List<WebMvcConfigurer> configurers) {
        if (!CollectionUtils.isEmpty(configurers)) {
            this.delegates.addAll(configurers);
        }
    }

// WebMvcAutoConfiguration的静态内部类 EnableWebMvcConfiguration
    @Bean
    @Primary
    @Override
    public RequestMappingHandlerMapping requestMappingHandlerMapping() {
        // Must be @Primary for MvcUriComponentsBuilder to work
        // 调用了WebMvcConfigurationSupport的requestMappingHandlerMapping
        return super.requestMappingHandlerMapping();
    }

// WebMvcConfigurationSupport.requestMappingHandlerMapping
    @Bean
    public RequestMappingHandlerMapping requestMappingHandlerMapping() {
        ···
        // 获取到interceptors
        mapping.setInterceptors(getInterceptors());
        ···
        return mapping;
    }

    protected final Object[] getInterceptors() {
        if (this.interceptors == null) {
            InterceptorRegistry registry = new InterceptorRegistry();
            // 调用子类DelegatingWebMvcConfiguration.addInterceptors
            addInterceptors(registry);
            registry.addInterceptor(new ConversionServiceExposingInterceptor(mvcConversionService()));
            registry.addInterceptor(new ResourceUrlProviderExposingInterceptor(mvcResourceUrlProvider()));
            this.interceptors = registry.getInterceptors();
        }
        return this.interceptors.toArray();
    }

// DelegatingWebMvcConfiguration.addInterceptors
    @Override
    protected void addInterceptors(InterceptorRegistry registry) {
        // WebMvcConfigurerComposite.addInterceptors
        this.configurers.addInterceptors(registry);
    }

// WebMvcConfigurerComposite.addInterceptors
  @Override
    public void addInterceptors(InterceptorRegistry registry) {
        for (WebMvcConfigurer delegate : this.delegates) {
            // 这里就可以调用用户自定义实现重写的WebMvcConfigurer.addInterceptors
            delegate.addInterceptors(registry);
        }
    }

zuul如何转发路由

// ServletWrappingController.handleRequestInternal
    @Override
    protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)
            throws Exception {

        Assert.state(this.servletInstance != null, "No Servlet instance");
        // 传入的是zuulServlet
        this.servletInstance.service(request, response);
        return null;
    }

// zuulServlet.service
    @Override
    public void service(javax.servlet.ServletRequest servletRequest, javax.servlet.ServletResponse servletResponse) throws ServletException, IOException {
        try {
            init((HttpServletRequest) servletRequest, (HttpServletResponse) servletResponse);

            // Marks this request as having passed through the "Zuul engine", as opposed to servlets
            // explicitly bound in web.xml, for which requests will not have the same data attached
            RequestContext context = RequestContext.getCurrentContext();
            context.setZuulEngineRan();


            // 之后就使用FilterProcessor对route的filter的进行过滤
            try {
                preRoute();
            } catch (ZuulException e) {
                error(e);
                postRoute();
                return;
            }
            try {
                route();
            } catch (ZuulException e) {
                error(e);
                postRoute();
                return;
            }
            try {
                postRoute();
            } catch (ZuulException e) {
                error(e);
                return;
            }

        } catch (Throwable e) {
            error(new ZuulException(e, 500, "UNHANDLED_EXCEPTION_" + e.getClass().getName()));
        } finally {
            RequestContext.getCurrentContext().unset();
        }
    }

// FilterProcessor类中
// 对zuulFilter进行过滤，sType为pre，route，post等 
    public Object runFilters(String sType) throws Throwable {
        if (RequestContext.getCurrentContext().debugRouting()) {
            Debug.addRoutingDebug("Invoking {" + sType + "} type filters");
        }
        boolean bResult = false;
        List<ZuulFilter> list = FilterLoader.getInstance().getFiltersByType(sType);
        if (list != null) {
            for (int i = 0; i < list.size(); i++) {
                ZuulFilter zuulFilter = list.get(i);
                Object result = processZuulFilter(zuulFilter);
                if (result != null && result instanceof Boolean) {
                    bResult |= ((Boolean) result);
                }
            }
        }
        return bResult;
    }

    public Object processZuulFilter(ZuulFilter filter) throws ZuulException {
        ···
        ZuulFilterResult result = filter.runFilter();
        ···
    }

// ZuulFilter.runFilter 调用各个子类实现至zuulFilter的run方法
    public ZuulFilterResult runFilter() {
        ZuulFilterResult zr = new ZuulFilterResult();
        if (!isFilterDisabled()) {
            if (shouldFilter()) {
                Tracer t = TracerFactory.instance().startMicroTracer("ZUUL::" + this.getClass().getSimpleName());
                try {
                    Object res = run();
                    zr = new ZuulFilterResult(res, ExecutionStatus.SUCCESS);
                } catch (Throwable e) {
                    t.setName("ZUUL::" + this.getClass().getSimpleName() + " failed");
                    zr = new ZuulFilterResult(ExecutionStatus.FAILED);
                    zr.setException(e);
                } finally {
                    t.stopAndLog();
                }
            } else {
                zr = new ZuulFilterResult(ExecutionStatus.SKIPPED);
            }
        }
        return zr;
    }